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Abstract Background Postmenopausal and the postpartum periods are essential physiological phases that result in low estrogen levels in women; however, they are important to female reproductive health. Traditional as well as new detection methods (such as 16 S RNA sequencing) have limitations in detecting the composition of vaginal microbiota. Therefore, in this study, we used metagenomic detection technology to study the composition of vaginal microbiota in postmenopausal and postpartum women. Six women were randomly selected from each group (healthy women of childbearing age, postmenopausal group, and postpartum) for vaginal microecology, composition, α-diversity, linear discriminant analysis effect size (LEfSe), and Comprehensive Antibiotic Resistance Database (CARD) analyses. Results We discovered that Lactobacillus dominance disappeared in postpartum and postmenopausal group women and that diversity increased. However, the proportions of Atopobium vaginae, Escherichia coli, and Streptococcus agalactiae significantly increased. Diversity was the highest in the postpartum period, with a significant increase in the proportions of A. vaginae, Gardnerella vaginalis, Prevotella, and occasionally, Chlamydia trachomatis. Linear discriminant analysis effect size analysis revealed that Lactobacillus crispatus and L. iners enrichment in the postpartum and menopausal periods was much lower than that in the childbearing age group. CARD analysis revealed that ABC-F ATP-binding cassette ribosomal protection protein subfamily gene abundance was significantly lower in the menopausal than in the childbearing age group, whereas the gimA family macrolide glycosyltransferase gene abundance was significantly higher. Conclusions The dominance of vaginal Lactobacillus in postpartum and menopausal women disappeared, while their diversity increased. In addition, the reproductive tract of postpartum women was susceptible to invasion by pathogenic microorganisms, which deserves clinical attention. When menopausal women receive treatment for vaginal infections, the likelihood that certain bacterial communities develop antibiotic resistance through ribosomal protection mechanisms is lower than that of women in the childbearing age, while the possibility of developing resistance to macrolides through glycosylation may increase. This, however, requires further research.